r - Smart way to chain ifelse statements?

Question

When I have to chain ifelse statements, it looks like:

ifelse(input=="x","x1",
       ifelse(input=="y","x2",
              ifelse(input=="z","x3",NA)))

Is there a smarter way to do this? I'm thinking about creating tables then merging or something alike just to make the code look better?

Answer 1

Apart from the suggestions in comments you could also use match in the following way.

Create sample data:

set.seed(1)
vals_in <- c("x", "y", "z")   # unique values in your input vector
vec_in <- sample(vals_in, 10, replace = TRUE)  # sample from vals_in to create input
vals_out <-  c("x1", "x2", "x3")  # values to replace

Now, to replace the nested ifelses you could do:

vec_out <- vals_out[match(vec_in, vals_in)]

The result is

vec_out
# [1] "x1" "x2" "x2" "x3" "x1" "x3" "x3" "x2" "x2" "x1"

---

A little comparison of two approaches:

set.seed(1)
vals_in <- letters
vec_in <- sample(vals_in, 1e7, replace = TRUE)
vals_out <-  LETTERS

system.time(vals_out[match(vec_in, vals_in)])
       User      System verstrichen 
      0.378       0.020       0.398 
system.time(unname(setNames(vals_out, vals_in)[vec_in]))
       User      System verstrichen 
      1.020       0.062       1.084